A typical cryogenic storage vessel includes an inner tank for retaining a supply of cryogenic fluid and an outer jacket or tank surrounding the inner tank to protect and thermally insulate the inner tank. Cryogenic liquid is stored in the lower portion of the inner tank while cryogenic gas forms in a head space of the inner tank as the cryogenic gas vaporizes. The outer tank is spaced from the inner tank to create a thermal insulation chamber therebetween. The thermal insulation chamber typically has a vacuum therein so that radiant and conductive heat transfer to the inner tank is reduced in order to reduce vaporization of the cryogenic liquid due to atmospheric thermal input.
Cryogenic storage vessels also often have a liquid level gauge that indicates a level of the cryogenic liquid within the inner tank. The most common type of liquid level gauge used in cryogenic storage vessels is a float-type liquid level gauge in which a float on a swing arm moves a spring-loaded dial as the float lowers and rises with the level of the cryogenic liquid. While these float-type liquid level gauges may perform in an adequate manner in many circumstances, their performance is less than ideal in other circumstances. For example, their performance is less than ideal in vertically-oriented cryogenic fluid cylinders where the longitudinal length of the cylinder is relatively large compared to the lateral diameter of the cylinder because the lateral diameter of the cylinder does not provide enough space so that swing arm can pivot over a desired portion of the length of the cylinder. Solutions have been to accept the less than desirable performance or to use more expensive and/or less reliable types of liquid level indicators. Accordingly, there is a need for improved liquid level gauges for cryogenic fluid storage vessels.